What is BMI?
Body Mass Index (BMI) is a measurement calculated from your height and weight that is used to screen for weight categories that may lead to health problems. It was developed in the 1830s and remains the most widely used initial screening tool worldwide.
BMI Formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lbs) ÷ height (inches)²
BMI Categories (WHO)
- Under 18.5 — Underweight
- 18.5 – 24.9 — Healthy weight
- 25.0 – 29.9 — Overweight
- 30.0+ — Obese
Limitations of BMI
BMI is a useful population-level screening tool but has limitations at the individual level. It doesn't differentiate between muscle and fat mass — a bodybuilder may have a high BMI despite low body fat. It also doesn't account for age, ethnicity, or fat distribution. Always consult a healthcare professional for a full health assessment.
Frequently Asked Questions
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, healthy ranges may vary slightly by age and ethnicity. Asian populations may have higher health risks at lower BMI values.
Is BMI accurate for athletes?
Not always. Athletes with high muscle mass may have a high BMI without being overweight. Muscle weighs more than fat, so BMI can overestimate body fat in muscular individuals. Body fat percentage tests provide a more accurate assessment.
How do I lower my BMI?
BMI can be reduced through a combination of a calorie-controlled diet and regular physical activity. A sustainable calorie deficit of 500 calories per day leads to approximately 0.5kg of weight loss per week.
What BMI is considered obese?
A BMI of 30 or above is classified as obese. Class I obesity is 30–34.9, Class II is 35–39.9, and Class III (severe obesity) is 40 or above.